Structure of graphene and a surface carbide grown on the (0001) surface of rhenium

Transition metal surfaces catalyse a broad range of thermally-activated\nreactions involving carbon-containing-species -- from atomic carbon to small\nhydrocarbons or organic molecules, and polymers. These reactions yield\nwell-separated phases, for instance graphene and the metal surface, or, on the\ncontrary, alloyed phases, such as metal carbides. Here, we investigate carbon\nphases on a rhenium (0001) surface, where the former kind of phase can\ntransform into the latter. We find that this transformation occurs with\nincreasing annealing time, which is hence not suitable to increase the quality\nof graphene. Our scanning tunneling spectroscopy and reflection high-energy\nelectron diffraction analysis reveal that repeated short annealing cycles are\nbest suited to increase the lateral extension of the structurally coherent\ngraphene domains. Using the same techniques and with the support of density\nfunctional theory calculations, we next unveil, in real space, the symmetry of\nthe many variants (two six-fold families) of a rhenium surface carbide observed\nwith diffraction since the 1970s, and finally propose models of the atomic\ndetails. One of these models, which nicely matches the microscopy observations,\nconsists of parallel rows of eight aligned carbon trimers with a so-called\n$(7\\times\\sqrt{\\mathrm{19}})$ unit cell with respect to Re(0001).\n